2 Plasmonics for Enhanced Vibrational Signatures
115
gold nanoparticles and aggregates can be up to 10 orders of magnitude. Isolated silver nanoparticles and silver nanoaggregates show basically the same behavior [59,
60]. The dramatic increase in field enhancement level can be explained by the interaction and hybridization of plasmons in adjacent nanoparticles [55]. Plasmonic field
enhancement exhibits particularly exciting properties for fractal metallic nanostructures [61–64].
Surface plasmon resonances for isolated particles strongly depend on their shape
and size. Advances in a controlled production of gold and silver nanoparticles make
it possible to tune their plasmon resonances over wide ranges in the visible and NIR.
Figure 2.5 summarizes representative tuning ranges for selected gold- and silver
nanostructures [65].
While plasmon resonances mainly cover the range between near ultraviolet (UV)
and near IR, further developing of SEIRA as a spectroscopic tool requires nanostructures which provide high field enhancement in the IR range. Nanoshells are very
interesting “single-particle” plasmonic structures exhibiting well-defined tunable
plasmon resonances over wide energy ranges down to the IR [66]. These structures are
of particular interest for the design of enhancing structures for SEIRA experiments
[31, 55, 67]. Also metal nanowires provide sufficiently strong antenna-like plasmonic resonances in the IR [29]. The resonance of the antenna can be adjusted to the
molecular vibration frequencies by changing the wire length. Arrays where antennae
can couple via nanogaps have been suggested and demonstrated as structures which
provide strong electromagnetic enhancement in the IR range [7, 30]. Vibration-signal
enhancement up to 500,000 have been obtained for molecular monolayers adsorbed
on gold nanowires.
Another methodological challenge in vibrational spectroscopy is plasmonic supported (resonance) Raman scattering using ultraviolet light for excitation. The extenFig. 2.5 Spectral dependence of the plasmon resonance of differently shaped silver and gold
nanoparticles (Reprinted with permission from [65])
115
gold nanoparticles and aggregates can be up to 10 orders of magnitude. Isolated silver nanoparticles and silver nanoaggregates show basically the same behavior [59,
60]. The dramatic increase in field enhancement level can be explained by the interaction and hybridization of plasmons in adjacent nanoparticles [55]. Plasmonic field
enhancement exhibits particularly exciting properties for fractal metallic nanostructures [61–64].
Surface plasmon resonances for isolated particles strongly depend on their shape
and size. Advances in a controlled production of gold and silver nanoparticles make
it possible to tune their plasmon resonances over wide ranges in the visible and NIR.
Figure 2.5 summarizes representative tuning ranges for selected gold- and silver
nanostructures [65].
While plasmon resonances mainly cover the range between near ultraviolet (UV)
and near IR, further developing of SEIRA as a spectroscopic tool requires nanostructures which provide high field enhancement in the IR range. Nanoshells are very
interesting “single-particle” plasmonic structures exhibiting well-defined tunable
plasmon resonances over wide energy ranges down to the IR [66]. These structures are
of particular interest for the design of enhancing structures for SEIRA experiments
[31, 55, 67]. Also metal nanowires provide sufficiently strong antenna-like plasmonic resonances in the IR [29]. The resonance of the antenna can be adjusted to the
molecular vibration frequencies by changing the wire length. Arrays where antennae
can couple via nanogaps have been suggested and demonstrated as structures which
provide strong electromagnetic enhancement in the IR range [7, 30]. Vibration-signal
enhancement up to 500,000 have been obtained for molecular monolayers adsorbed
on gold nanowires.
Another methodological challenge in vibrational spectroscopy is plasmonic supported (resonance) Raman scattering using ultraviolet light for excitation. The extenFig. 2.5 Spectral dependence of the plasmon resonance of differently shaped silver and gold
nanoparticles (Reprinted with permission from [65])